* {
    box-sizing: border-box;
  }
  
  body {
    font-family: 'Ubuntu', sans-serif;
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    overflow: hidden;
    margin: 0;
  }
  
  .bg {
    background: url('https://pic1.zhimg.com/v2-eff9ea4cdc44cd6b92532dd52e3e4100_r.jpg?source=1940ef5c')
      no-repeat center center/cover;
    position: absolute; /*脱离文档流后原来的位置相当于是空的，下面的元素会来占据位置。*/
    top: -15px;
    left: -15px;
    width: calc(100vw + 30px);/*加上30px是为了让图片全部覆盖浏览器窗口*/
    height: calc(100vh + 30px);
    z-index: -1; /*让图片在加载进度的下面*/
  }
  
  .loading-text {
    font-size: 50px;
    color: #fff;
  }